While there has been significant progress in management of early stages of clear cell renal cell carcinoma (RCC), metastatic RCC has few effective therapeutic strategies available and a death rate close to the incidence. Targeted therapies, particularly angiogenesis inhibitors such as sunitinib, have shown efficacy against metastatic RCC. Nonetheless, sunitinib treatment invariably leads to resistance, necessitating novel, more efficacious therapies. We have taken advantage of the Connectivity Map (C-Map) database, a compendium of gene expression profiles of cancer cell lines treated with a spectrum of small molecules, to test our hypothesis that drugs that elicit gene signatures most opposed to sunitinib resistance are likely to overcome, delay or prevent resistance to sunitinib in RCC. Transcriptome analysis of RCC xenografts treated with sunitinib enabled us to generate a sunitinib resistance gene signature that was applied to the C-Map database, resulting in identification of a ranking list of drugs anticipated to reverse most prominently the hypoxia-driven pro-angiogenic sunitinib resistance gene signature. We demonstrated that three of the highest ranking, FDA-approved candidate drugs, maprotiline, terazosin and clemastine, indeed reverse the sunitinib resistance gene signature in RCC cells, including various genes involved in angiogenesis. In order to move an actionable drug closer to a clinical trial we will, therefore, perform a preclinical assessment of the most promising drug, maprotiline, to prevent, delay or overcome sunitinib resistance in RCC xenografts, and determine predictors of therapeutic response as companion diagnostics and pharmacodynamics markers. Detailed mechanistic analysis of anti-RCC action for maprotiline will determine whether maprotiline-mediated suppression of pro-angiogenic factors is critical for reversing escape from sunitinib response, and whether maprotiline-mediated direct anti-oncogenic efficacy against RCC is a consequence of downregulation of miR- 21 and enhanced expression of pro-apoptotic genes. In Specific Aim 1 we will determine predictors of therapeutic response and the molecular mechanisms of anti-RCC action for maprotiline. In Specific Aim 2 preclinical in vivo assessment of maprotiline will determine whether maprotiline is able to prevent, delay or overcome sunitinib resistance. Our proof-of-concept data demonstrate that our strategy enables rapid discovery of new anti-cancer properties for drugs not typically used in cancer treatment. The demonstration of anti-tumor efficacy in small animal cancer models is a key bridge from in vitro studies to human clinical testing. In particular, if a drug is already approved for another indication, proceeding with clinical testing might require only a compelling in vitro storyline supported by a limited number o animal studies demonstrating in vivo anti-tumor efficacy. Since maprotiline is FDA-approved, clinical trials combining standard of care sunitinib with maprotiline could be rapidly initiated upn successful completion of the animal experiments.